The present applicant suggests an atmosphere continuous furnace for burning refractory products, an example of which is shown in Patent Document 1. As illustrated in Patent Document 1, this type of continuous furnace (see FIG. 5) includes a to-be-burned object path 14 surrounded by an in-furnace ceiling 11, an in-furnace side wall 12, and an in-furnace floor 13. The to-be-burned object path 14 includes, in an order from the inlet to the outlet, a medium-to-low-temperature zone, a high-temperature zone, and a cooling zone through which the to-be-burned object is burned while being moved in this order. The path is designed so that atmosphere gas flows from the outlet to the inlet. The furnace is generally designed so that the in-furnace gas is exhausted through an exhaust duct (not shown) provided in the medium-to-low-temperature zone at a position close to the inlet.
Patent Document 1: JP 2003-207274 A (claims and FIG. 1)
When the continuous furnace having the structure as described above accommodates a to-be-burned object that contains an alkaline component such as Na or K, the alkaline component vaporizes in the high-temperature zone. This has caused a disadvantage where the in-furnace gas containing this alkaline component deteriorates the refractory products (11, 12, 13) constituting the furnace, causing a reduced service life of the furnace.
In the case of a to-be-burned object containing a metal Si component and a highly-fire-resistant to-be-burned object mainly containing SiC or Si3N4, SiO caused by the oxidization thereof in a low-oxygen atmosphere gas environment vaporizes to partially turn into SiO2 that is attached to an in-furnace ceiling surface and a side wall face. These components change, when combined with the alkaline component, to a strong glass-like solid substance that is accumulated on the in-furnace ceiling surface and the side wall face. This has caused a disadvantage where the operation of the to-be-burned object is hindered or the exhaust performance is significantly deteriorated. A risk has been also caused by SiO's strong oxidation reactivity to cause a case where SiO attached to the interior of the exhaust duct may oxidize to generate heat for example.
The present invention has been made in order to solve the above-described disadvantages. In particular, the present invention provides the exhaust method and the exhaust structure of the continuous furnace by which a to-be-burned object containing a metal Si component, a highly-fire-resistant SiC-containing ceramics, and Si3N4-containing ceramics are prevented from causing vaporized SiO attached to the in-furnace ceiling or the wall for example so that safe and easy exhaust can be achieved.